Water-dispersible hybrid polymer

Abstract: Proposed is a water-dispersible hybrid polymer comprising an ethylenically unsaturated polyurethane (core) onto which an addition polymer chain (shell) has been provided by polymerisation, with the unsaturation of the polyurethane being achieved by the incorporation therein of dimethyl-m-isopropenyl benzyl isocyanate, and the acid number of the shell polymer being in the range of 30 to 120 (mg KOH/g). Aqueous dispersions of these hybrid polymers are pre-eminently suitable for use in aqueous coating compositions of the so-called clear coat type, particularly when stringent demands are imposed with regard to the acid resistance of the topcoats applied using these compositions.

Description: The invention relates to a water-dispersible hybrid polymer comprising an ethylenically unsaturated polyurethane (core) onto which an addition polymer chain (shell) has been provided by polymerisation, to an aqueous dispersion incorporating such a polymer, and to the use of such a dispersion in coating compositions. A water-dispersible hybrid polymer of the aforementioned type is known from WO-A-91/15 528. In WO-A-91/15 528, the ethylenically unsaturated groups in the polyurethane originate from a polyester polyol and/or a polyether polyol and/or a compound which in addition to an ethylenically unsaturated group shows a group reactive toward NCO groups. As examples of suitable ethylenically unsaturated compounds may be mentioned trimethylol propane monoallyl ether, glycerol monoallyl ether, pentaerythritol diallyl ether, and alkenedicarboxylic acids, such as maleic acid and unsaturated dimerised fatty acids. The compositions disclosed in said document are recommended exclusively for use in coating compositions of the so-called base coat type. They were found to be less suitable for use in coating compositions of the so-called clear coat type, particularly when stringent demands are imposed with regard to the acid resistance of topcoats applied using these compositions. The current invention now provides a water-dispersible hybrid polymer which is not only suitable for use in the same applications as listed in WO-A-91/15 528, but is also pre-eminently suitable for use in coating compositions of the clear coat type. In this invention, a water-dispersible hybrid polymer of the known type mentioned in the opening paragraph, the polyurethane unsaturation has been achieved by the incorporation therein of 0,05 to 1 mole dimethyl-m-isopropenyl benzyl isocyanate per mole of polyurethane, and the acid number of the shell polymer is in the range of 30 to 120 (mg KOH/g). Upon dispersal in an aqueous medium, the hybrid polymers according to the invention were found, after neutralisation of at least a portion of the carboxyl groups of the addition polymer chains by a base, to yield a stable dispersion of a comparatively low viscosity, even at a concentration of 40 wt.% and higher and with an average particle size of 100 nm or even less. The hybrid polymers themselves have a relatively low acid number comparable to the acid number of polymers used in organic solvents. Aqueous dispersions of these hybrid polymers are suited to be used in aqueous coating compositions with a comparatively high solids content. Films obtained with such coating compositions have favourable mechanical and physical properties and were also found to possess good resistance to attack by water, chemicals, and acids. Good resistance to acids was found to be of great importance in the case of use in topcoats of the so-called clear coat type. The hybrid polymer according to the invention preferably is made up of 40-90 wt.% of core and 10-60 wt.% of shell. Within these limits, the hybrid polymer was found to possess the optimum combination of the individual components' advantageous properties. Among the advantageous properties of polyurethanes are favourable mechanical characteristics and good resistance to acids. The good resistance to chemical action and hydrolysis is mainly due to the composition of the shell made up of addition polymers. The core Particularly suitable polymers are hybrid polymers of which the core is comprised of a polyurethane prepared from a diol and aliphatic, cycloaliphatic and/or araliphatic diisocyanates. As examples of suitable diisocyanates may be mentioned: tetramethylene-1,4-diisocyanate, hexamethylene-1,6-diisocyanate, cyclohexyl-1,4-diisocyanate, isophorone diisocyanate, dicyclohexyl methane-4,4'-diisocyanate, 1,5-dimethyl-2,4-bis(isocyanatomethyl)benzene, 1,5-dimethyl2,4bis(ω-isocyanatoethyl)benzene, 1,3,5-trimethyl-2,4-bis(isocyanatomethyl)benzene, 1,3,5-triethyl-2,4-bis(isocyanatomethyl)benzene, and dicyclohexyl dimethylmethane-4,4'-diisocyanate. In general, preference is given to polyurethanes based on non-aromatic diisocyanates, since polyurethanes based on aromatic diisocyanates are subject to discolouration by UV radiation. In coating compositions for topcoats which are not brought into contact with UV radiation, such as filler and primer, hybrid polymers of which the core is comprised of aromatic diisocyanates may be utilised with advantage. Examples of suitable aromatic diisocyanates include toluene diisocyanate and diphenyl methane-4,4'-diisocyanate. Linear as well as branched diols with 2-12 carbon atoms are suitable for use. Examples of suitable diols include: glycol, 1,3-propane diol, 1,6-hexane diol, 1,12-dodecane diol, 3-methyl-1,5-pentane diol, 2,2,4-trimethyl-1,6-hexane diol, 2,2-dimethyl-1,3-propane diol, and 2-methyl-2-cyclohexyl-1,3-propane diol. Also, ester diols may be used. As an example thereof may be mentioned the neopentylglycol ester of hydroxypivalic acid. In addition, polyester diols may be used, provided they have a low acid number (less than 5 mg KOH/g). They are preferably prepared from aromatic and/or cycloaliphatic dicarboxylic acids or derivatives thereof and the aforementioned diols. The term derivatives of (cyclo)aliphatic or aromatic dicarboxylic acids refers to the anhydrides or the alkyl esters having alkyl groups of 1-4 carbon atoms thereof. As suitable (cyclo)aliphatic or aromatic dicarboxylic acids or derivatives thereof may be mentioned: tetrahydrophthalic acid, tetrahydrophthalic anhydride, phthalic anhydride, endomethylene tetrahydrophthalic acid, hexahydrophthalic anhydride, hexachloroendomethylene tetrahydrophthalic acid, hexahydrophthalic acid, hexahydroterephthalic acid, phthalic acid, p-carboxymethyl benzene acid, dichlorophthalic acid, tetrachlorophthalic acid, dimethyl terephthalate, dimethyl hexahydroterephthalate, naphthalene-2,6-dicarboxylic acid, and 4,4'-oxydibenzoic acid. Particularly preferred are dicarboxylic acids having 8-10 carbon atoms, e.g. isophthalic acid and terephthalic acid. When the hybrid polymers according to the invention are used in topcoats of the clear coat type, preference is given to (cyclo)aliphatic dicarboxylic acids, since this will improve resistance to ultraviolet radiation. Favourable results have further been obtained using polyester diols prepared by the conversion of a half ester of the aforementioned diols with a (cyclo)aliphatic or aromatic dicarboxylic anhydride and a monoepoxide such as 1,2-epoxy-octane or, preferably, a glycidyl ester of a carboxylic acid according to the formula below: wherein R 1 is an alkyl group having 4-40 carbon atoms. Optimum results were found to be obtained when the polyurethane is comprised of: a) n moles of diisocyanate, b) n+1 moles of diol having an acid number < 5 (mg KOH/g) and a molecular weight (Mn) of 70 - 2000, with n = 1-10, and c) 0,05 - 1,0 mole of dimethyl-m-isopropenylbenzyl isocyanate. Besides diisocyanates, triisocyanates may be used for the preparation of the water-dispersible hybrid polymers according to the present invention. Examples of suitable triisocyanates include: the reaction product of 3 moles of hexamethylene-1,6-diisocyanate and 1 mole of H 2 O (marketed by Bayer under the trade designation Desmodur N), the isocyanurate trimer of hexamethylene-1,6-diisocyanate (Desmodur N® 3390 ex Bayer or Tolonate HDT® ex Rhône-Poulenc), the isocyanurate trimer of isophorone diisocyanate, and the reaction product of 1 mole of trimethylol propane and 3 moles of isophorone diisocyanate. For polyurethanes based on triisocyanates, optimum results were found using: a) 1 mole of triisocyanate, b) 3 - 3,6 moles of diol having an acid number < 5 (mg KOH/g) and a molecular weight (Mn) of 70 - 2000, with the two hydroxyl groups of the diol exhibiting different reactivities toward isocyanate groups, and c) 0,05 - 1,0 mole of dimethyl-m-isopropenylbenzyl isocyanate. In order to prevent gelling when employing a triisocyanate, it is important that the diol or polyester diol contains two OH groups which each have a different reactivity toward isocyanate. Examples of diols having OH groups of different reactivities include: 2-ethyl-1,3-hexane diol, 2-methyl-1,3-hexane diol, 2-propyl-1,3-hexane diol, 2-butyl-2-ethylpropane diol-1,3, as well as the polyester diols prepared from a half ester of a linear or branched diol having 2-12 carbon atoms and 2 primary OH groups and a (cyclo)aliphatic or aromatic dicarboxylic anhydride and a monoepoxide such as 1,2-epoxyoctane or, preferably, a glycidyl ester of a carboxylic acid according to Formula I below: wherein R 1 is an alkyl group having 4-40 carbon atoms. To prevent gelling it is of importance that the dimethyl-m-isopropenylbenzyl isocyanate be used in an amount of less than 1 mole per mole of polyurethane. Preference is given in this case to using 0,05 - 0,6 moles per mole of polyurethane if the polyurethane has been prepared with a disocyanate, and to using 0,05 - 0,4 moles per mole of polyurethane when the latter has been prepared from a triisocyanate. However, the optimum amount to be used of said ethylenically unsaturated monoisocyanate is also dependent on the monomers to be employed in the preparation of the shell, the initiator, and the use of a chain length regulator, if any. The polyurethane is prepared in a dry atmosphere at a temperature in the range of 50° to 120°C, preferably in the range of 60° to 100°C. Optionally, use may be made of a catalyst such as an amine or an organometallic (e.g., tin) compound in the conventional amount of 0,01 to 0,1 wt.%. As stabiliser or inhibitor may be employed hydroquinone, hydroquinone monomethyl ether, nitrobenzene or ditertiary-butylphenol in the conventional amount of 50 to 1000 ppm. The shell The hybrid polymer is prepared by addition polymerisation of monomers polymerisable under the influence of radicals in the presence of an ethylenically unsaturated polyurethane described hereinbefore. In this process the addition polymer chains are covalently bonded to the polyurethane by means of copolymerisation with the ethylenically unsaturated bond. The monomers polymeriserisable under the influence of radicals for the addition polymer chains may be chosen from a wide range, including ethylenically unsaturated monocarboxylic acids such as (meth)acrylic acid and crotonic acid; (cyclo)alkyl (meth)acrylates having 1-12 carbon atoms in the (cyclo)alkyl group, such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isobornyl (meth)acrylate, dodecyl (meth)acrylate, and cyclohexyl (meth)acrylate; dicarboxylic acids, such as maleic acid (and anhydride), fumaric acid, itaconic acid (and anhydride); (cyclo)alkyl esters of such dicarboxylic acids having 1-12 carbon atoms in the (cyclo)alkyl group, such as dimethyl maleate, diethyl maleate, diethyl fumarate, dipropyl maleate, dibutyl maleate, dibutyl fumarate, 2-ethylhexyl maleate, 2-ethylhexyl fumarate, octyl maleate, isobornyl maleate, dodecyl maleate, and cyclohexyl maleate; (meth)acrylates with ether groups, such as 2-methoxy-ethyl methacrylate, 2-ethoxyethyl methacrylate, and 3-methoxy-propyl methacrylate; hydroxyalkyl (meth)acrylates, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl acrylate, 6-hydroxyhexyl acrylate, p-hydroxycyclohexyl (meth)acrylate; hydroxypolyethylene glycol (meth)acrylates; hydroxypolypropylene glycol (meth)acrylates and alkoxy derivatives thereof; monovinyl aromatic compounds, such as styrene, vinyl toluene, α-methyl styrene, and vinyl naphthalene; other substituted (meth)acrylate compounds, such as (meth)acrylamide, (meth)acrylonitrile, N-methylol (meth)acrylamide, and N-alkyl (meth)acrylamides; other mono-unsaturated compounds, such as vinyl chloride, vinyl acetate, vinyl propionate, and vinyl pyrrolidone. For monomer mixtures which are pre-eminently suited to form the addition polymer chains reference is made to EP-B-0 000 601. The following monomer mixture is a specific example from said publication: 25-55 mole% of styrene and/or α-methyl styrene, 20-40 mole% of a compound according to formula (2): wherein: R 2 represents a hydrogen atom or a methyl group, and R 3 represents an alkyl group having 4-40 carbon atoms, 10-30 mole% of acrylic acid and/or methacrylic acid, and 0-30 mole% of some other mono-unsaturated compound as described hereinbefore. Another specific example of a monomer mixture disclosed in EP-B-0 000 601 is as follows: 25-55 mole% of styrene and/or α-methyl styrene, 20-50 mole% of acrylic acid and/or methacrylic acid, and 0-30 mole% of some other mono-unsaturated compound as described hereinbefore, wherein, during or after polymerisation, the reaction product is reacted with such an amount of glycidyl ester of a carboxylic acid according to Formula I as will give an acid number for the obtained shell polymer in the range of 30 to 120 (mg KOH/g). As stated above, the specific monomers and monomer mixtures should be so chosen as to ensure that the resulting shell polymer has an acid number in the range of 30 to 120 (mg KOH/g). When the acid number is less than 30, it generally proves to be impossible to obtain a stable dispersion, while the water resistance of the dispersion proves unacceptable if the acid number is higher than 120. Of course, the selection of the monomers and/or monomer mixtures is dependent on various factors, including the final application of the hybrid polymer. In actual practice, it is quite easy for the person of average skill in the art to take these and other factors into account and adjust the monomers' selection in line with the envisaged use. The copolymerisation of the ethylenically unsaturated monomers in the presence of the ethylenically unsaturated polyurethane is generally carried out in an inert atmosphere (e.g. of nitrogen) and in the presence of a radical initiator. The polymerisation temperature may range from 60° to 200°C, preferably from 100° to 160°C. As suitable radical initiators may be mentioned: 2,2-azobis-2-methylbutyronitrile, 2,2-azobisisobutyronitrile, dibenzoyl peroxide, dicumyl peroxide, methyl ethyl ketone peroxide, cumene hydroperoxide, tert.butyloxy-2-ethyl hexanoate, tert.butyl perbenzoate, tert.butylcumyl peroxide, di-tert.butyl peroxide, di-tert.butylperoxy-3,5,5-trimethyl cyclohexane, 1,3-bis(tert.butyl)peroxyisopropyl benzene. Mixtures of the above-mentioned initiators are also suitable for use. In general, the radical initiators are employed in an amount of about 0,05 wt.% to about 10 wt.%, preferably of about 1 wt.% to 5 wt.%, based on the overall weight of the monomer mixture. Optionally, use may also be made of a chain length regulator such as n-octyl mercaptan, dodecyl mercaptan or 3-mercaptopropionic acid. It is preferred to carry out the polymerisation reaction in an organic solvent (10-30 wt.%) at a temperature of 60° to 200°C. The organic solvent used in this reaction should be water-miscible. Suitable examples of such a solvent are glycol ethers and propylene glycol ethers, such as methoxypropanol, butoxyethanol, isopropanol, diethylene glycol monobutyl ether, diethylene glycol monomethyl ether, propoxypropanol, diethylene glycol dimethyl ether, and N-methyl pyrrolidone. Alternatively, it is possible to employ small amounts of a water-immiscible organic solvent, e.g., ethylmethyl ketone and methyl isobutyl ketone. Dispersions of hybrid polymers The invention also relates to aqueous dispersions of the hybrid polymers described hereinbefore. These are readily dispersible in an aqueous medium after at least a portion of the carboxyl groups of the addition polymer chains has been neutralised. The group of suitable neutralisation agents for carboxyl groups comprises a wide range of organic and inorganic bases. As examples may be mentioned ammonia, primary, secondary, and tertiary amines, such as ethyl amine, propyl amine, dimethyl amine, dibutyl amine, cyclohexyl amine, benzyl amine, morpholine, piperidine, and triethanol amine. The use of tertiary amines, such as dimethylethanol amine, triethyl amine, tripropyl amine, and tributyl amine, is preferred. The degree of neutralisation preferably is 50 to 130% on the basis of equivalency. Following neutralisation the hybrid polymers can easily be dispersed in an aqueous medium in a conventional manner, preferably at elevated temperatures in the range of 50° to about 100°C. When hybrid polymers according to the invention are employed, in many cases stable dispersions having a solids content of 40 wt.% and even higher may be obtained. Coating compositions of dispersions of hybrid polymers As was stated earlier, dispersions of hybrid polymers are preeminently suited to be used in coating compositions. When the dispersions of hybrid polymers according to the invention are so utilised, the coating compositions may also contain a curing agent for curing via the hybrid polymer's hydroxyl groups. Films of coating compositions according to the invention were found to exhibit outstanding physical and mechanical properties, such as flexibility, hardness, and gloss. As suitable curing agents may be mentioned, in general, N-methylol- and/or N-methylol ether-containing aminoplasts. Favourable results are attained when using methylol melamine containing 4-6 methylol groups per molecule, with at least three of the methylol groups being esterified with methanol, butanol and/or a methanol or butanol condensation product of formaldehyde and N,N'-ethylene diureum. Other appropriate curing agents include water-dispersible blocked isocyanates, e.g., those blocked with methylethyl ketoxime, and isocyanate group-containing adducts of a polyisocyanate and a hydrocarboxylic acid, e.g. dimethylpropionic acid. As a rule, the curing agents which react with the hydroxyl groups are employed in such an amount as will give a ratio of the number of hydroxyl groups in the hybrid polymer to the number of reactive groups of the curing agent in the range of 0,7 to 1,5. Depending on their field of application, the coating compositions may contain a variety of other additives common to the paint industry, such as pigments, colouring agents, pigment dispersing agents, and thixotropic or other rheological agents. If so desired, the coating composition may also contain accelerators for the curing reaction, such as p-toluene sulphonic acids and blocked derivatives thereof. The coating compositions according to the invention may be applied onto any known substrate such as wood, synthetic materials, and metals. Suitable application methods include rolling, spraying, sprinkling, dipping, and electrostatic spraying. Of course it is also possible to apply the coating composition by simple brushing. The coating composition may be dried and cured under a variety of conditions, e.g. at room temperature. Accelerated curing may be accomplished by baking at elevated temperatures in the range of 100° to 160°C over a period of 20 to 60 minutes. These coating compositions are suitable for use in a wide range of applications. They are especially suitable, however, for use as primer/filler, and clear and coloured paints. The invention will be further illustrated with reference to a number of non-limiting examples. Examples In the following examples a number of stable aqueous polymer dispersions were prepared in accordance with the invention. Various properties of these dispersions were measured, the results being listed in TABLE 1. For instance, the average particle size of the dispersion was determined by dynamic light scattering, the dispersions being diluted to a solids content of 0,1 wt.%. The viscosity was determined with a Brookfield viscometer (LV - 4; 60 rpm). The solids content of the dispersions was measured in accordance with ASTM method 1644-59, with heating to 140°C over a period of 30 minutes. Preparation of the dispersions Polyurethanes having a molecular weight of about 2000 to 4000 of theory were prepared from diol intermediates and a polyisocyanate, with dibutyl tin diacetate (DBTDA) being used as catalyst. The three diol intermediates (intermeiates A-C) described below were employed. intermediate A: In a 3 l flask fitted with a stirrer, a thermometer, a cooler, and a dropping funnel a mixture was homogenised, the mixture comprised of: 236 g of 1,6-hexane diol 208 g of neopentyl glycol 616 g of cis-hexahydrophthalic anhydride, and 6 g of benzyl triphenyl phosphonium chloride. The dropping funnel was filled with 1000 g of the glycidyl ester of 1,1-dimethyl-1-heptane carboxylic acid (Cardura E-10®, ex Shell). After ventilation, the flask and the dropping funnel were brought under a nitrogen atmosphere. The contents of the flask were heated to 120°C. After 1 hour of reaction at this temperature, the contents of the flask were heated to 140°C. The contents of the dropping funnel were added dropwise to the flask over a period of 2 hours. After 4 hours, the reaction mixture had an acid number of 8,5 (mg KOH/g resin). Next, 80 g of Cardura E-10® were added. After 2 hours, the acid number of the reaction mixture was < 1 (mg KOH/g resin). The molecular weight of the thus prepared intermediate was 537 of theory. intermediate B: In a 3 l flask fitted with a stirrer, a thermometer, a cooler, and a dropping funnel a mixture was homogenised, the mixture comprised of: 265,5 g of 1,6-hexane diol 234,0 g of neopentyl glycol 666,0 g of phthalic anhydride, and 6,8 g of benzyl triphenyl phosphonium chloride. The dropping funnel was filled with 1125 g of Cardura E-10®. After ventilation, the flask and the dropping funnel were brought under an atmosphere of nitrogen. The contents of the flask were heated to 136°C. The contents of the dropping funnel were added dropwise to the flask over a period of 1,5 hours. After 3 hours, the reaction mixture had an acid number of 9,7 (mg KOH/g resin). Next, 100 g of Cardura E-10® were added. After 2 hours, the acid number of the reaction mixture was <1 (mg KOH/g resin). The molecular weight of intermediate B was 533 of theory. intermediate C : A resin was prepared in a manner analogous to that indicated for product B, except that the molecular weight of the intermediate this time was 520 of theory. Example I In a 2 l flask fitted with a stirrer, a thermometer, a reflux condenser, and two dropping funnels a mixture was homogenised, the mixture comprised of: 261,6 g of intermediate A 55,0 g of N-methyl pyrrolidone (NMP) 0,1 g of DBTDA. The first dropping funnel was filled with 72,1 g of isophorone diisocyanate (IPDI), and the second one was filled with 16,3 g of dimethyl-m-isopropenyl benzyl isocyanate (m-TMI®) (ex Cyanamid). Barring air humidity, the contents of the flask were heated to 90°C. After 1 hour, the contents of the first dropping funnel were added dropwise to the flask. After 2 hours of reaction at 90°C, the reaction mixture was heated to 100°C. Over a period of 15 minutes the contents of the second dropping funnel were added dropwise to the flask. The reaction mixture was subsequently kept at this temperature for 1 more hour. Next, one dropping funnel was replaced with a third dropping funnel filled with a homogeneous mixture of: 38,2 g of styrene, 9,2 g of methyl methacrylate, 33,1 g of acrylic acid, 66,0 g of Cardura E-10®, 2,7 g of dicumyl peroxide, 0,8 g of 3-mercaptopropionic acid, and 51,9 g of 2-butoxyethanol. After ventilation, the flask and the dropping funnel were brought under an atmosphere of nitrogen. The contents of the flask were heated to 130°C. The contents of the dropping funnel were added dropwise to the flask over a period of 1 hour. The reaction mixture was kept at this temperature for 3 hours. After cooling to 115°C, 18,1 g of N,N-dimethyl ethanolamine were added. After cooling to 90°C, 782 g of demineralized water were added dropwise to the flask over a period of 3 hours, with vigorous stirring of the flask's contents. Example II In a manner analogous to that indicated in Example I a polymer dispersion was prepared, except that this time use was made of the following ingredients: 286,0 g of intermediate A 50,0 g of NMP, and 0,1 g of DBTDA. The first dropping funnel was filled with 59,7 g of hexamethylene diisocyanate (HDI). The second dropping funnel was filled with 14,3 g of m-TMI®. The first reaction was carried out at 80°C. The third dropping funnel was filled this time with a homogeneous mixture of: 30,6 g of styrene, 7,3 g of methyl methacrylate, 26,4 g of acrylic acid, 52,8 g of Cardura E-10® 2,2 g of dicumyl peroxide, 0,7 g of 3-mercaptopropionic acid, and 45,1 g of 1-methoxypropanol-2. On conclusion of the reaction, 14,5 g of N,N-dimethyl ethanolamine and 711,8 g of demineralized water were added. Example III In a manner analogous to that indicated in Example I a polymer dispersion was prepared, except that this time the flask was filled with the following ingredients: 283,0 g of intermediate A, 40,0 g of NMP, and 0,1 g of DBTDA. The first dropping funnel was filled with 66,4 g of HDI. The second dropping funnel was filled with 10,6 g of m-TMI®. The third dropping funnel was filled with a homogeneous mixture of: 7,3 g of methyl methacrylate, 26,4 g of acrylic acid, 52,8 g of Cardura E-10®, 2,2 g of dicumyl peroxide, 0,7 g of 3-mercaptopropionic acid, and 32,0 g of 1-methoxypropanol-2. On conclusion of the reaction, 14,5 g of N,N-dimethyl ethanolamine and 604,2 g of demineralized were added. Example IV In a manner analogous to that indicated in Example I a polymer dispersion was prepared, except that this time the flask was filled with the following ingredients: 281,3 g of intermediate A, 40,0 g of NMP, and 0,1 g of DBTDA. The first dropping funnel was filled with 70,3 g of HDI. The second dropping funnel was filled with 8,4 of m-TMI®. The third dropping funnel was filled with a homogeneous mixture of: 30,6 g of styrene, 7,3 g of methyl methacrylate, 26,4 g of acrylic acid, 52,8 g of Cardura E-10®, 2,2 g of dicumyl peroxide, 0,7 g of 3-mercaptopropionic acid, and 32,0 g of 1-methoxypropanol-2. On conclusion of the reaction, 14,5 g of N,N-dimethyl ethanolamine and 604,2 g of demineralized water were added dropwise. Example V In a manner analogous to that indicated in Example I a polymer dispersion was prepared, except that this time the flask was filled with the following ingredients: 280,7 g of intermediate B, 40,0 g of NMP, and 0,1 g of DBTDA. The first dropping funnel was filled with 70,8 g of HDI. The second dropping funnel was filled with 8,5 g of m-TMI®. The third dropping funnel was filled with a homogeneous mixture of: 30,6 g of styrene, 7,3 g of methylmethacrylate, 26,4 g of acrylic acid, 52,8 g of Cardura E-10®, 2,2 g of dicumyl peroxide, 0,7 g of 3-mercaptopropionic acid and, 32,0 g of 1-methoxypropanol-2. On conclusion of the reation, 14,5 g of N,N-dimethyl ethanolamine and 549,8 g of demineralized water were added. Example VI In a manner analogous to that indicated in Example I a polymer dispersion was prepared, except that this time the flask was filled with the following ingredients: 333,5 g of intermediate C and 0,45 g of DBTDA. The first dropping funnel was filled with a homogeneous mixture of: 106,7 g of Tolonate HDT® (ex Rhône-Poulenc) (isocyanurate trimer of hexamethylene-1,6-diisocyanate) and 60,0 g of NMP. The second dropping funnel was filled with 9,8 g of m-TMI®. Barring air humidity, the contents of the flask were heated to 80°C. The contents of the first dropping funnel were added dropwise to the flask over a period of 1 hour. After 3 hours of reaction at 80°C, the reaction mixture was heated to 100°C. The contents of the second dropping funnel were added dropwise to the flask in 15 minutes. The reaction mixture was subsequently kept at this temperature for 1 more hour. Next, one dropping funnel was replaced with a third dropping funnel, which was filled with a homogeneous mixture of: 38,1 g of styrene, 9,2 g of methyl methacrylate, 33,0 g of acrylic acid, 65,9 of Cardura E-10®, 2,75 g of dicumyl peroxide, 1,10 g of 3-mercaptopropionic acid, and 30,0 g of diethylene glycol monobutyl ether. Following ventilation, the flask and the dropping funnel were brought under an atmosphere of nitrogen. The contents of the flask were heated to 130°C. Over a period of 1 hour the contents of the dropping funnel were added dropwise to the flask. The reaction mixture was kept at this temperature for 3 hours. After cooling to 115°C, 16,8 g of N,N-dimethyl ethanolamine were added. After cooling to 90°C, 1006 g of demineralized water were added dropwise over a period of 2 hours. Example VII In a manner analogous to that indicated in Example VI a polymer dispersion was prepared, except that this time the third dropping funnel was filled with: 36,7 g of styrene, 11,5 g of 2-hydroxyethyl methacrylate, 31,7 g of acrylic acid, 66,1 g of Cardura E-10®, 2,6 g of dicumyl peroxide, 1,3 g of 3-mercaptopropionic acid, and 30,0 g of diethylene glycol monobutyl ether. On conclusion of the reaction, 16,8 g of N,N-dimethyl ethanolamine and 914,8 g of demineralized water were added. Example VIII In a manner analogous to that indicated in Example VII a polymer dispersion was prepared, except that this time the flask was filled with the following ingredients: 335,0 g of intermediate C, and 0,45 g of DBTDA. The first dropping funnel was filled with a homogeneous mixture of: 107,2 g of Tolonate HDT®, and 60,0 g of NMP. The second dropping funnel was filled with 7,8 g of m-TMI®. On conclusion of the reaction, 16,8 g of N,N-dimethyl ethanolamine and 793,2 g of demineralized water were added. Example IX In a manner analogous to that described in Example VII a polymer dispersion was prepared, except that this time the flask was filled with the following ingredients: 336,5 g of intermediate C, and 0,45 g of DBTDA. The first dropping funnel was filled with a homogeneous mixture of: 107,6 g of Tolonate HDT®, and 60,0 g of NMP. The second dropping funnel was filled with 5,9 g of m-TMI®. On conclusion of the reaction, 16,8 g of N,N-dimethyl ethanolamine and 721,8 g of demineralized water were added. Example X In a manner analogous to that indicated in Example VII a polymer dispersion was prepared, except that this time the flask was filled with the following ingredients: 337, 9 g of intermediate C, and 0,45 g of DBTDA. The first dropping funnel was filled with a homogeneous mixture of: 108,1 g of Tolonate HDT®, and 60,0 g of NMP. The second dropping funnel was filled with 3,9 g of m-TMI®. On conclusion of the reaction, 16,8 g of N,N-dimethyl ethanolamine and 612,0 g of demineralized water were added. Example XI In a manner analogous to that indicated in Example VII a polymer dispersion was prepared, except that this time the flask was filled with the following ingredients: 339,2 g of intermediate A, and 0,45 g of DBTDA. The first dropping funnel was filled with a homogeneous mixture of: 105,1 g of Tolonate HDT®, and 60,0 g of NMP. The second dropping funnel was filled with 5,7 g of m-TMI®. On conclusion of the reaction, 16,8 g of N,N-dimethyl ethanolamine and 721,8 g of demineralized water were added. Example XII In a 2 l flask fitted with a stirrer, a thermometer, a reflux condenser, and two dropping funnels a mixture was homogenised, the mixture comprised of: 190 g of 2-ethyl-1,3-hexane diol, and 0,45 g of DBTDA. The first dropping funnel was filled with a homogeneous mixture of: 238,3 g of Tolonate HDT®, and 60 g of NMP. The second dropping funnel was filled with 21,8 g of dimethyl-m-isopropenyl benzyl isocyanate (m-TMI®). Barring air humidity, the contents of the flask were heated to 70°C. The contents of the first dropping funnel were added dropwise to the flask over a period of 1 hour, the contents of the flask being kept at 70°C. After 3 hours of reaction at 70°C, the reaction mixture was heated to 100°C, after which the contents of the second dropping funnel were added dropwise to the flask in 15 minutes. The reaction mixture was subsequently kept at 100°C for 1 more hour. Next, one dropping funnel was replaced with a third dropping funnel which was filled with a homogeneous mixture of: 37,5 g of styrene, 11,45 g of methyl methacrylate, 32,95 g of acrylic acid, 65,80 g of Cardura E-10®, 2,75 g of dicumyl peroxide, 1,35 g of 3-mercaptopropionic acid, and 30,00 g of diethylene glycol monobutyl ether. After ventilation, the flask and the dropping funnel were brought under an atmosphere of nitrogen, after which the contents of the flask were heated to 130°C. The contents of the dropping funnel were added dropwise to the flask in 1 hour, the contents of the flask being kept at 130°C. The reaction mixture was kept at this temperature for 3 hours. After cooling to 115°C, 18,5 g of N,N-dimethyl ethanolamine were added. After cooling to 90°C, 830 g of demineralized water were added dropwise over a period of 2 hours, with vigorous stirring of the flask's contents. Example XIII In a manner analogous to that indicated in Example XII a polymer dispersion was prepared, except that this time the third dropping funnel was filled with a homogeneous mixture of: 34,3 g of styrene, 14,3 g of 2-hydroxyethyl methacrylate, 31,6 g of acrylic acid, 65,9 g of Cardura E-10®, 2,6 g of dicumyl peroxide, 1,3 g of 3-mercaptopropionic acid, and 30,0 g of diethylene glycol monobutyl ether. On conclusion of the reaction, 16,8 g of N,N-dimethylethanolamine and 793 g of demineralized water were added. Example XIV In a manner analogous to that indicated in Example XIII a polymer dispersion was prepared, except that this time the second dropping funnel was filled with 17,6 g of m-TMI®. On conclusion of the reaction 16,8 g of N,N-dimethyl ethanolamine and 756 g of demineralized water were added. The properties of the polymer dispersions prepared as specified in the examples above are listed in TABLE 1 below. Dispersion of Example Solids content (wt.%) Viscosity (Pa.s.) pH average particle size (nm) I 35,8 1,1 8,6 71 II 36,0 0,4 8,6 81 III 40,3 0,9 8,6 71 IV 40,4 0,7 8,5 70 V 43,1 0,5 8,6 78 VI 33,8 0,6 8,6 156 VII 36,2 1,2 8,4 125 VIII 39,3 1,2 8,5 112 IX 41,9 0,5 8,5 64 X 43,8 1,0 8,3 83 XI 41,0 0,4 8,4 67 XII 38,1 0,5 8,5 99 XIII 39,5 2,5 8,5 66 XIV 40,2 0,6 8,5 67 Preparation of coating compositions Examples XV-XXXV below cover the preparation of a number of unpigmented coating compositions according to the invention by mixing the dispersion, a melamine hardener, and demineralized water, if desired. The melamine hardeners used in these examples were Cymel 303® and Cymel 327® ex Cyanamid. When Cymel 303® was used, p-toluene sulphonic acid blocked with diethanol amine was employed as catalyst. The demineralised water was added to adjust the viscosity to a spraying viscosity of 0,1 Pa.s. (run-out viscosity of 30 s. in a Ford Cup No. 4). The solids content of these coating compositions was determined in the same way as that of the dispersions. The results are given in TABLE 2. coating compositions Example Disp. Disp. (g) Cymel 327® (g) Cymel 303® (g) p-TSZ (g) solids content (wt.%) XV ExI 70 30 - - 39,7 XVI ExI 80 - 20 0,3 35,7 XVII ExII 70 30 - - 41,8 XVIII ExIII 70 30 - - 45,0 XIX ExIV 70 30 - - 45,9 XX ExV 70 30 - - 46,3 XXI ExVI 70 30 - - 37,2 XXII ExVI 80 - 20 0,3 39,2 XXIII ExVII 75 25 - - 38,7 XXIV ExVIII 75 25 - - 40,7 XXV ExIX 75 25 - - 42,7 XXVI ExIX 75 - 25 0,25 41,0 XXVII ExX 75 25 - - 44,2 XXVIII ExX 75 - 25 0,25 44,3 XXIX ExXI 75 25 - - 42,2 XXX ExXI 70 30 - - 42,6 XXXI ExXII 75 25 - - 40,2 XXXII ExXIII 75 25 - - 40,8 XXXIII ExXIII 80 - 20 0,3 38,5 XXXIV ExXIV 75 25 - - 42,3 XXXV ExXIV 75 - 25 0,25 39,3 Each of the coating compositions was applied onto a steel panel (Bonder 132) pretreated with zinc phosphate and cured for 30 minutes in a baking oven of 140°C in the case of Cymel 327® being used, and of 130°C when Cymel 303® was employed. Various properties of the thus obtained coating compositions were measured, and the results are listed in TABLE 3. The Persoz hardness was determined in accordance with French industrial standard NF T30-016, with the result being expressed in seconds. An acceptable minimum for automotive paints is about 180 seconds. The flexibility of the coating compositions was determined with the ball impact test in accordance with ASTM D2794-69, using a ball weight of 0,908 kg, a ball diameter of 15,9 mm, and an aperture of 16,3 mm. The results are expressed in kg.cm. An acceptable minimum flexibility is 35 kg.cm for the coated side, the maximum measurable value being 85 kg.cm. In addition, the Erichsen indentation test was performed. The results are expressed in mm. A value > 6 indicates that the tested coat is flexible, while a value of 2 indicates that it is brittle. The gloss of the coating composition was determined in accordance with ASTM D-523 at 60° and 20°. A gloss value on a steel substrate > 80 measured at 60° is considered high. properties of the topcoats applied using the coating compositions Coating composition of example Layer thickness (µm) Persoz hardn. sec Flexibility (kg.cm) Erichsen indentation (mm) Gloss coated side uncoated side 60° 20° XV 40 312 22 <2 6,6 92 76 XVI 42 271 46 2 8,4 94 80 XVII 40 202 85 83 8,6 92 76 XVIII 39 202 66 >85 7,7 92 76 XIX 40 223 >85 >85 7,8 92 77 XX 40 235 78 85 7,4 92 77 XXI 41 301 58 46 7,3 94 74 XXII 41 194 >85 >85 8,6 94 76 XXIII 41 251 >85 >85 7,5 94 74 XXIV 41 234 85 >85 7,9 98 80 XXV 40 237 >85 >85 7,6 96 80 XXVI 45 326 25 5 7,0 95 70 XXVII 42 210 80 80 7,7 95 79 XXVIII 40 325 28 5 7,7 94 67 XXIX 41 161 >85 >85 7,5 95 80 XXX 39 225 68 64 7,4 94 79 XXXI 41 299 56 20 7,8 95 77 XXXII 41 286 46 34 7,5 95 77 XXXIII 42 302 28 5 7,0 95 77 XXXIV 40 289 44 28 7,6 96 79 XXXV 42 309 32 7 7,0 95 78 The results of TABLE 3 show that the hybrid polymers according to the invention can be used to prepare coating compositions which upon application onto a substrate will yield topcoats exhibiting favourable properties, such as high hardness, high flexibility, and high gloss. Acid resistance To determine resistance to acids, several unpigmented coating compositions were applied onto aluminium test panels and cured as indicated hereinbefore. After curing, the topcoats all had a layer thickness of about 40 µm. To carry out the test, 5 drops each of a 38 wt.% and a 52 wt.% H 2 SO 4 solution, respectively, were applied to the panel to be tested, which was then visually assessed for any attack after 4, 8, and 16 hours. The results of this assessment are given on a scale of 0 to 10. On this scale 10 indicates that the panel has not been subject to any attack at all, while 0 stands for serious damage. 10 : no damage 7 - 9 : clearly visible stain 4 - 6 : clouding of the film 0 - 3 : cracked and damaged film The results of the measurements are given in TABLE 4 below. Topcoats of several commercially available, organic solvent-containing coating compositions have been incorporated into the testing programme as references. Ref. 1 is composed of: 70 wt.% of acrylate based on: 32,5 wt.% of 2-hydroxyethyl acrylate 28,0 wt.% of styrene 18,5 wt.% of butyl acrylate 21,0 wt.% of butyl methacrylate (Mn = 3000), and 30 wt.% of hexamethoxymethyl melamine (Cymel 303®) (acid catalysed) Ref. 2 is composed of: 70 wt.% of acrylate based on: 33,5 wt.% of 2-hydroxypropyl methacrylate 20,0 wt.% of butyl methacrylate 13,0 wt.% of styrene 1,5 wt.% of methacrylic acid 32,0 wt.% of butyl acrylate (Mn = 3000), and 30 wt.% of hexamethoxymethyl melamine (Cymel 303®) (acid catalysed) Ref. 3 is composed of: 70 wt.% of Ref. 1 acrylate and 30 wt.% Cymel 327® Ref. 4 is composed of: 70 wt.% of Ref. 2 acrylate and 30 wt.% Cymel 327® Coating composition of Example Assessment of acid resistance 38 wt.% H 2 SO 4 52 wt.% H 2 SO 4 4hr 8hr 16hr 4hr 8hr 16hr XVIII 10 9 7 8 2 0 XIX 10 8 5 9 5 2 XX 10 10 10 10 8 5 XXI 10 10 10 10 10 10 XXII 10 10 10 10 10 10 XXIII 10 10 10 10 10 10 XXIV 10 10 10 10 10 10 XXV 10 10 10 10 10 10 XXVI 10 10 10 10 10 10 XXVII 10 10 10 10 10 10 XXVIII 10 10 10 10 10 10 XXIX 10 10 10 10 10 10 XXX 10 10 10 10 10 10 XXXI 10 10 10 10 10 10 XXXII 10 10 10 10 10 10 XXXIII 10 10 10 10 10 8 XXXIV 10 10 10 10 10 10 XXXV 10 10 9 10 8 5 Ref.1 10 5 3 8 3 0 Ref.2 10 5 3 7 2 0 Ref.3 10 5 2 7 2 0 Ref.4 10 4 1 7 2 0 The test results listed in TABLE 4 clearly show that the topcoats obtained with the coating compositions according to the present invention invariably contrast surprisingly favourably with the topcoats obtained with the reference samples. It can also be concluded from the test results in the above table that the coating compositions based on Examples XXI to XXXIV, all of which were prepared from a triisocyanate based polyurethane, generally generate the best results.

Claims: A water-dispersible hybrid polymer comprising an ethylenically unsaturated polyurethane core onto which an addition polymer chain shell has been provided by polymerisation, characterised in that the unsaturation of the polyurethane has been achieved by the incorporation therein of 0,05 to 1 mole of dimethyl-m-isopropenyl benzyl isocyanate per mole of polyurethane, and the acid number of the shell polymer is in the range of 30 to 120 (mg KOH/g). A water-dispersible hybrid polymer according to claim 1, characterised in that the polymer is made up of 40-90 wt.% of core and 10-60 wt.% of shell. A water-dispersible hybrid polymer according to claim 1, characterised in that the polyurethane is comprised of: a) n moles of diisocyanate, b) n+1 moles of diol having an acid number < 5 (mg KOH/g) and a molecular weight (Mn) of 70 - 2000, with n = 1-10, and c) 0,05 - 1,0 mole of dimethyl-m-isopropenyl benzyl isocyanate. A water-dispersible hybrid polymer according to claim 1, characterised in that the polyurethane is comprised of: a) 1 mole of triisocyanate, b) 3 - 3,6 moles of diol having an acid number < 5 (mg KOH/g) and a molecular weight (Mn) of 70 - 2000, with the two hydroxyl groups of the diol exhibiting different reactivities toward isocyanate groups, and c) 0,05 - 1,0 mole of dimethyl-m-isopropenyl benzyl isocyanate. A water-dispersible hybrid polymer according to claim 3 or 4, characterised in that the diol is 2-ethyl-1,3-hexane diol. A water-dispersible hybrid polymer according to claim 3 or 4, characterised in that the diol is the reaction product of a half ester of a diol having 2 primary OH groups and 2-12 carbon atoms and a (cyclo)aliphatic or aromatic dicarboxylic anhydride and a monoepoxide such as 1,2-epoxyoctane or, preferably, a glycidyl ester of a carboxylic acid according to the formula: wherein R 1 represents an alkyl group having 4-40 carbon atoms. A water-dispersible hybrid polymer according to claim 1, characterised in that the polymer of the shell is comprised of: 25-55 mole% of styrene and/or α-methyl styrene, 20-50 mole% of acrylic acid and/or methacrylic acid, and 0-30 mole% of some other monounsaturated compound, followed by conversion with such an amount of glycidyl ester of a carboxylic acid of the formula in claim 6 as will give an acid number for the shell polymer in the range of 30 to 120 (mg KOH/g). A water-dispersible hybrid polymer according to claim 1, characterised in that at least a portion of the carboxyl groups of the shell polymer is neutralised with a base. An aqueous dispersion based on a water-dispersible hybrid polymer according to claim 8. A coating composition based on an aqueous dispersion according to claim 9.

Inventors: BUTER ROELOF, ROELOFS ANDREAS HENRICUS JOHAN, BUTER, ROELOF, ROELOFS, ANDREAS HENRICUS JOHANNES
Applicants: AKZO NOBEL NV, AKZO NOBEL N.V.
Application year: 1994
Main classification: C08F283
IPC codes: C08L75, C08G18, C08L25, C08L51, C09D151, C08L73, C08F283